The first thing you should think about is what exactly you mean when you keep talking about your "old self." Life is fluid and dynamic, and we are always growing and changing as people (for better or for worse). I think what you mean is that you miss the stability you once had. Perhaps you also have a longing for a time of innocence too, before you feel like your mind got corrupted by heroin and all of the darkness that is in the surrounding lifestyle. As an artist, I'm sure that your moods and emotions affect your output, and perhaps you don' feel like your emotions are in line with the art you've brainstormed about making in the past. And you wish you could get back into that mentality. But ya, the tough news that is that after a heroin addiction, life isn't ever really the same. Unlike other drugs or mistakes made, this actually is a life-changing thing. It's a big deal, and lying to yourself about its magnitude will only make it worse. This doesn't have to be a bad thing, as you can find new things to help you move forward and help yourself that you may have never otherwise gotten into (for me, I got really into Eastern spirituality recently, and it helps me stay clean). But you need to just try and focus on the present and making each day/week/month slightly better than the last one. The past is over, we cannot ever reclaim it. I'm guilty of the same thing...I've had money, cars, city apartments, living abroad, scholarships, etc, and lost it all to heroin. When I think too much about it, I want to cry and shake, so I just hide the photos, don't talk to people from that era, and so on. I just try and be happy that I have a job and a roof over my head at all today. I knot that this kind of advice can come off as annoying, so I hope it doesn't that much to you!
If you're a girl by yourself in a new city and you're struggling with heroin, it can turn really bad really quickly in a couple different ways. I won't spell them out here for you, but basically the physical dependency never stops, and sometimes streams of money do. People scramble impulsively, vultures watch people like you within the game, etc. As herbivore said, you need something of an escape plan put into place right now, today, in case you find yourself falling very fast. You need a place to go outside of the city with people who won't judge you and where you can detox.
You can try out NA meetings if you want to. Personally, I want to stay as far away from them as possible, but I did at least try them out. A lot of people will tell you that you have a disease, that you are weak and cannot do this alone, and so on. They'll also tell you that it's not about will-power. I actually think that we as "addicts" completely and totally have the power to do it from the inside-out, and that it actually is completely about will-power. You know yourself best and you want the better life. Don't sell yourself short, go get it! I'd see you as an artist with an imagination who wants to explore her senses and try out new things. You got curious about drugs and how they'd affect how you felt and your creative output, and you continued on into heroin and it turned out to be absolutely relentless. If you want to call yourself an "addict" and whatnot, and you don't find that patronizing, then go for it. But I'd instead continue to look at yourself as an artist. You'll need the art to propel yourself forward from here.
Check this artist out for some inspiration!